Significance: Proteases make up 2% of the human proteome (3), and their functional activity is a unique, irreversible post-translational modification of their target substrates (7). Proteases are involved in a number of important physiological functions from blood coagulation to digestion and pathophysiological activities necessary for activation and propagation of cancer cascades and Alzheimer's disease (8). More information about protease biology and pathophysiology in addition to new selective therapeutics would be important for understanding and treating human disease.